Little fruit fly makes big impact on berry growers

It’s just a little fruit fly that hadn’t even been seen in this country until 2008 when it turned up in California. But a year later, the spotted winged drosophila appeared in Florida. And then, shortly after Hurricane Irene hit New England in September 2011, the pest was first seen here in the Pioneer Valley.

Last year, some growers noticed that the tiny bug was getting into their raspberries and blueberries, leaving the fruit slightly mushy. And this summer, with a statewide trapping and monitoring program already detecting a small presence of the Southeast Asian native, the University of Massachusetts Extension website is calling the spotted wing drosophila the “pest of the year.”

The fly, which appears to over-winter on a variety of wild plants like grapes, pokeweed, and wild blueberries on the woody edges of cultivated fields, making it more difficult for farmers to manage, is peskier than the fruit flies that hover around kitchen counters, according to Extension fruit specialist Sonia Schloemann.

“The thing that makes them difficult is they have the ability to lay eggs in fruit that hasn’t been damaged by something else,” like punctures from hail or birds.

Unlike most pests, for which there’s generally time to prepare and do research, Schloemann said, “This one hit us pretty quickly, so we’re learning about it at the same time we’re having to deal with it.”

For blueberry and raspberry growers, it’s important to get their ripe fruit harvested as soon as possible, which presents a challenge for those farmers who have depended heavily on pick-your-own sales.

“Any lag between picks, when you’re having (ripe) fruit hanging out in the field, that’s the fruit that’s vulnerable,” Schloemann said, stressing the importance of paying close attention to what’s happening and to details like managing leaf canopy that limits air circulation and sunlight. The fruit flies prefer moist, shady environments, so thinning leaves and pruning bushes so light can penetrate is important, as is seeing that harvested fruit is refrigerated rather than being left to sit in flats or boxes.

Crops at risk include everything from blackberries and elderberries to some plums, peaches, strawberries, apples and even high-tunnel tomatoes, but Extension fruit specialist Jon Clements said it’s blueberries and raspberries that seem to be most threatened, particularly because the insect population swells as the season progresses.

“It’s a nightmare,” said Whately berry farmer Fran Sobieski, who began his pick-your-own blueberry operation this week in hopes of getting the season off to an earlier start. “Last year, it didn’t wipe us out completely, but it made it really rough. Before, the main problem was birds. Now they’re number two.”

Sobieski, who grows about eight acres of berries, said Schloemann’s advice about moving out fruit after it ripens may be sound, but he added, “There’s no way we can do that,” in part because his raspberry bushes were planted 35 years ago in rows as narrow as 8½ feet apart, and when their limbs begin to bear down heavy with fruit, it’s hard to get in and clean out the ripened berries.

“We’re pushing like crazy, earlier than we would have,” said Sobieski. “The fruit is fantastic and tasty this year. All that rain’s helped.”

Although researchers are working on a variety of approaches to attack the newly arrived pest, including parasites and traps that attract and collect the adults before the fruit begins to ripen, Schloemann said that for now, “The ultimate tool will have to be spraying. It’s sort of an unfortunate reality.”

The good news is that the spray that seems most effective, available commercially as Entrust, is safe enough to be approved for certified organic use.

Timothy Nourse of Whately’s Nourse Farms, which has already begun its you-pick season for raspberries and plans to begin blueberry picking as well this weekend, said he sprayed last year to control the fruit flies, and is beginning to do the same this season.

“It’s a big problem,” he said of the pests, which can have over 10 generations in a single growing season. “They multiply by the gazillions We’ve been working so long as (integrated pest management) growers, reducing our use of pesticides, but they’re out all over the place, and this is the only way to keep those little worms out of the fruit.”

Heath grower Andrew Kurowski of The Benson Place, said that with more than 30 acres of wild blueberries, and another 20 acres of rented fields, keeping up with ripening fruit will be another challenge, added to problems like the frost that ruined last year’s crops, as well as nibbling grasshoppers and birds and the sawfly that eats the leaves of the bushes in spring.

Kurowski, who hopes to open his you-pick operation July 27, said he’s also planning to experiment with sugar-and-yeast lures to trap and control the population. Yet he, too, plans to spray.

Meanwhile, Clements said, “I think it’s a controllable problem, but it will take some extra effort to control it, and there will be an added cost for pesticides and for labor. We were caught off guard, but it’s become so common, you’re going to get it if you don’t take some action. We’re going to have to live with it, to a certain extent, and to deal with it.”